Ultraviolet photochemical nitridation of GaAs

Abstract

Monolayer nitridation of Ga-rich GaAs(100) is achieved at 100 K by simultaneous exposure to ammonia and 6.4 eV photons in a vacuum environment. This process is a result of nonthermal photodissociation of adsorbed ammonia. Surface NH2 is identified as an important intermediate in nitridation.

Nitridation of GaAs (001) Surface Studied by Auger Electron Spectroscopy

“…The intensity of that peak diminishes drastically with an increase in the nitridation temperature, the peak becoming indiscernible in the spectra taken at T s = 600 • C. On the basis of the previous XPS results the peak at the low-KE side of the As-originated spectra has been attributed to the surface AsN species, and the disappearance of this peak at T s ≥ 500 • C is caused by desorption of the AsN species from the surface. [6][7][8] It should be noted that our results show that the AsN-originated peak is discernible in the spectra up to the nitridation temperature of 500 • C, which is in contradiction with the previous XPS results showing a complete disappearance of that peak for T s ≥ 300 • C. This discrepancy, however, can be explained by a difference in the experimental protocols used. Indeed, the XPS measurements have been carried out after the nitridation was interrupted for some finite period of time, the period of time long enough for the desorption of AsN from the nitrided surface for T s ≥ 300 • C. On the other hand, our measurements have been carried out simultaneously with the nitridation process and, therefore, the magnitude of the AsN-originated peak in our case shows the amount of AsN on the surface resulting from a dynamic equilibrium between the two processes, i.e.…”

“…As it has been verified by XPS studies, [5][6][7][8]14) nitridation of the GaAs (001) surface results in the formation of the disordered Ga-As-N compound as incoming N atoms substitute for the As atoms. The formation of the Ga-As-N phase leads to the broadening of the Auger signals and is partly responsible for the observed shifts in the spectra.…”

“…The formation of Ga-N and As-N bonds on the GaAs (001) surface during nitridation has been verified by infrared reflectance spectroscopy, where a hot tungsten filament was used to supply active nitrogen species, 4) as well as by X-ray photoelectron spectroscopy (XPS), where nitrogen 5) or ammonia 6) plasmas, and photolyzing of pre-adsorbed ammonia, 7,8) were used as methods to obtain the active nitrogen. The published XPS results show the chemical shifts of the core levels of gallium, arsenic and nitrogen caused by the ni-active nitrogen species with the As-stabilized GaAs (001)-2 × 4 surface at various surface temperatures in the range from room temperature (RT) to 600 • C. The measurements at all temperatures studied have been carried out simultaneously with the nitridation process, providing, thereby, an insight into the process of nitridation not hindered by the "postnitridation" relaxation effects.…”

Photoemission spectroscopy studies of the surface of GaN films grown by vapor phase epitaxy

“…Different groups do not even agree on the binding energy of Ga͑3d͒ core levels. [13][14][15][16][17][18][19] In this Letter, we report a study of the surface of GaN films grown by halide vapor phase epitaxy ͑HVPE͒ using synchrotron radiation angle-integrated photoemission spectroscopy. Our measurements indicate that the variability in results obtained by different groups is related to contaminants on and the stoichiometry of the surface of GaN.…”

“…[6][7][8][9][10][11] They have been compared with optical measurements 12 and limited photoemission spectroscopy measurements. [13][14][15][16][17][18][19] There have as yet been no systematic measurements on surfaces of GaN that are believed to be clean. Different groups do not even agree on the binding energy of Ga͑3d͒ core levels.…”